The present invention relates to liquid crystal displays and particularly to field effect liquid crystal displays which are illuminated for improved night visibility.
The prior art includes various solid state watches with liquid crystal displays. These displays in some instances have been provided with an illuminated background to enhance nighttime visibility. Nevertheless, the displays suffer from a significant degradation in appearance during daytime due to the use of a translucent diffuser incorporated in the design which fails to reflect a sufficient amount of incident light to the viewer. Such displays would, therefore, appear dark or relatively ill-defined in comparison with the display of the present invention.
Representative of the prior art is U.S. Pat. No. 3,731,986 to Fergason which issued May 8, 1973 on display devices using liquid crystal light modulation. Fergason discloses the use of either crossed or uncrossed polarizers on opposite sides of the nematic liquid crystal material but he does not disclose the features of the present invention which enhance nighttime viewing. Similarly, the disclosure of U.S. Pat. No. 3,592,526 to Dryer which issued July 13, 1971, discloses a light transmissive device for twisting the plane of polarization of polarized light by rotating the walls of a liquid crystal cell.
Bergey U.S. Pat. No. 3,722,206 issued Mar. 27, 1973 discloses a self-illuminated liquid crystal timepiece including liquid crystals disposed between a clear front glass and a dark back reflector glass and a nuclear powered light source surrounding the display face to provide light under dark conditions. Neither the polarizers or reflecting arrangement of the present invention are disclosed.
U.S. Pat. No. 3,799,647 to Luft discloses a constant visibility electro-optic display using a PLZT material rather than a liquid crystal material. The display includes an electro-optic plate having a partially transparent reflector plate mounted behind the plate and a pair of polarizers on either side of the arrangement, whereas the relationship of reflectors and polarizers is different in the present invention and the reflector comprises generally a layer of deposited material.
Also of interest is U.S. Pat. No. 3,668,861 to Mitsui, issued June 13, 1972, disclosing a watch having a liquid crystal display system operable at high levels of ambient illumination and a solid state system operable at low levels of ambient illumination. Further prior art in the general area of the invention includes U.S. Pat. No. 3,499,702 to Goldmacher et al., issued Mar. 10, 1970 and U.S. Pat. No. 3,625,591 to Freiser, issued Dec. 7, 1971. The patents cited above are, of course, not intended to be an all inclusive listing of pertinent patents since other patents of such nature may exist.